Localized network service

ABSTRACT

A method for providing a network service to a plurality of mobile terminals inside a service area, the mobile terminals being arranged to communicate with a cellular communication network and the service area being a part of a geographical area that is covered by the cellular communication network, the method comprising the steps of defining a grid with grid lines, the grid covering the service area with one or more tiles framed by the grid lines; determining whether there is at least one split tile that results from splitting the one or more tiles along closer grid lines and that does not overlap with the service area; splitting the one or more tiles along the closer grid lines based on the determining; and providing the network service in the split tiles that cover the service area.

CROSS REFERENCE TO RELATED APPLICATIONS

This application is a continuation of U.S. patent application Ser. No.14/652,990, filed 17 Jun. 2015, which itself is a 35 U.S.C. §371national stage application of PCT International Application No.PCT/EP2012/076128, filed on 19 Dec. 2012, the disclosure and content ofwhich is incorporated by reference herein in its entirety. Theabove-referenced PCT International Application was published in theEnglish language as International Publication No. WO 2014/094843 A1 on26 Jun. 2014.

TECHNICAL FIELD

The present invention relates to providing a network service to aplurality of mobile terminals that are arranged to communicate with acellular communication network. The present invention specificallyrelates to providing a network service in tiles of a grid that cover aservice area in which said network service is to be provided. Thepresent invention also relates to a corresponding network entity, acorresponding network system, a corresponding computer program, and acorresponding computer program product.

BACKGROUND

It is known to provide so-called Location Based Services (LBS) incellular communication networks, such as a cellular wireless telephonenetwork. Such services typically comprise a mechanism for estimating thelocation of a mobile terminal, e.g. with the help of satellite-basedpositioning systems (GPS, Galileo, Glonass, etc.) and/or a MobilePositioning System (MPS). Said LBS mechanisms are known to enablecontent delivery based on the location of a user or a vehicle (mobileterminal). Based on the knowledge of the mobile terminal's location,specific location based services can be offered to said mobile terminal,e.g. alert messages for upcoming road traffic hazards or indicationstoward deviations to avoid traffic jams. In these examples the user is avehicle with a respective mobile terminal on board.

It is further known to broadcast information with the help of so-calledCell Broadcast Services (CBS), in order to distribute information tomobile terminals within one or more cells. The respective mobileterminals have to enable the listening of the respective broadcastchannel. A so-called Multimedia Broadcast and Multicast Service (MBMS)is known that provides a broadband broadcast to mobile terminals.

Such data communication in cellular communication networks is dominatedby using a request response communication mechanism that is triggered bythe mobile terminal, or point-to-point (P2P) data communication usingShort Message Service (SMS) and Multimedia Message Service (MMS).Further, said LBS technologies or the aforementioned broadcasttechnologies are being introduced for enabling an enriched requestresponse communication.

One possible implementation of an LBS uses a grid formed by crossinggrid lines so as to define grid fields, or tiles, that are framed by thegrid lines. Usually, four grid lines form at least one tile of asquare-like, rectangular, or any 4-polygon-like shape. The grid, thegrid lines, and the tiles can be defined so as to cover a given servicearea with one or more tiles. Said service area may consist of one ormore contiguous areas of arbitrary shape in which said network serviceis to be provided. An example can be a circular service area covering aroad intersection. In general, the service area is independent from thegrid, the grid lines, and thus also from the tiles.

Such network services may involve information indicting the position andthe extension of the grid lines, crossing information indicating that amobile terminal has crossed a grid line, i.e. indicating that the mobileterminal has entered a specific tile, and tile information for keepingtrack of what mobile terminals are currently inside a given tile. Saidinformation concerning the grid lines may be conveyed to the mobileterminals so that a crossing of one grid line can be detected by themobile terminal. Such crossing may trigger the generating and sending tothe network side (e.g. a responsible target network entity) of saidcrossing information. Correspondingly the network side can keep track ofwhat mobile terminal(s) are in what tile for maintaining said tileinformation.

When the network service is to send any information (e.g. a message,such as a traffic hazard warning) to some or all mobile terminals thatare currently inside a given service area, it can be referred to thetile information so as to determine all the mobile terminals that areinside the tiles that cover the specific service area. Referring to saidtile information can also yield an identification of all the targetmobile terminals. Thus, messages can be then sent only to these targetmobile terminals ensuring that the right terminals are addressed, e.g.the ones that may be affected by a warning, and that—at the sametime—unnecessary communication to mobile terminals outside the servicearea is avoided.

Such conventional concepts usually deploy tiles with a fixed size sothat a constant number of tiles cover a given service area. Acorresponding exemplary situation is shown in conjunction with FIG. 2A,in which the four tiles 101, 102, 103, and 104, formed by crossing gridlines 1101 to 1105, cover an exemplary service area 200. In suchsituations, the tiles are assumed to be constant and to not to take intoaccount any detailed relation between the service area and the actualtiles. For example, the tile 104 of FIG. 2A overlaps with the servicearea 200 only by a small fraction.

In any way, the actual tile size may have significant impacts onsignalling capacity and/or messaging overhead. As a consequence, theoverall bandwidth required by the network service may depend on the tilesize. For example, messages may be sent to all terminals inside tile 104although most of the terminals that are located inside tile 104 may notbe inside the service area 200.

Therefore, there is a need for a method of providing a network service,and corresponding network entities, network systems, computer programs,and computer program products that take into account the dependence ofthe required bandwidth of the network service (i.e. radio and processingresources) on actual tile size. Such a solution is desirable, since lessbandwidth may be needed, resulting in—amongst others—a saving in thetotal cost of ownership.

SUMMARY

The above-mentioned problems and drawbacks of the conventional conceptsare solved by the subject-matter of the independent claims. Furtherpreferred embodiments are defined in the dependent claims.

According to an aspect of the present invention, a method is providedfor providing a network service to a plurality of mobile terminalsinside a service area, the mobile terminals being arranged tocommunicate with a cellular communication network and the service areabeing a part of a geographical area that is covered by the cellularcommunication network. The method comprises the steps of defining a gridwith grid lines, the grid covering the service area with one or moretiles framed by the grid lines; determining whether there is at leastone split tile that results from splitting the one or more tiles alongcloser grid lines and that does not overlap with the service area;splitting the one or more tiles along the closer grid lines based on thedetermining; and providing the network service in the split tiles thatcover the service area.

According to another aspect of the present invention, a network entityis provided for providing a network service to a plurality of mobileterminals inside a service area, the mobile terminals being arranged tocommunicate with a cellular communication network and the service areabeing a part of a geographical area that is covered by the cellularcommunication network. The network entity comprises a processing unitthat is configured to define a grid with grid lines, the grid coveringthe service area with one or more tiles framed by the grid lines;determine whether there is at least one split tile that results fromsplitting the one or more tiles along closer grid lines and that doesnot overlap with the service area; split the one or more tiles along thecloser grid lines based on the determination whether there is at leastone split tile; and to provide the network service in the split tilesthat cover the service area.

According to another aspect of the present invention, a network systemis provided in which a network service is provided to a plurality ofmobile terminals, wherein the network system comprises a network entityof one of the embodiments of the present invention.

According to another aspect of the present invention, a computer programis provided that comprises code, the code, when executed on a processingunit, instructing the processing unit to perform a method embodiment ofthe present invention.

According to yet another aspect of the present invention, a computerprogram product is provided that stores code, the code, when executed ona processing unit, instructing the processing unit to perform a methodembodiment of the present invention.

BRIEF DESCRIPTION OF THE DRAWINGS

Embodiments of the present invention, which are presented for betterunderstanding the inventive concepts but which are not to be seen aslimiting the invention, will now be described with reference to theFigures in which:

FIG. 1A shows a schematic representation of an in-field implementationof a network service according to an embodiment of the presentinvention;

FIG. 1B shows a schematic view of a network system architectureaccording to another embodiment of the present invention;

FIGS. 2A to 2C show in a schematic fashion the splitting of tiles inline with embodiments of the present invention;

FIG. 3 shows a possible timely evolution of the signalling and payloadversus time;

FIGS. 4A and 4B show different broadcast scenarios in terms of broadcastcapacity versus time;

FIG. 5 shows a flowchart representation of method embodiments of thepresent invention;

and

FIG. 6 shows a schematic view of a network entity in communication witha network according to another embodiment of the present invention.

DETAILED DESCRIPTION

Firstly, the basic concept of a localized network service (LBS) isdescribed with the example of travelling vehicles as shown with FIG. 1A.In this example, vehicles 11, 12, and 13 travel along a road, such as amulti-lane highway. The vehicles may have access to asatellite-supported positioning service 40, such as the ones known byGlobal Positioning System (GPS), Galileo, Glonass, or other servicesthat allow for a determination of a terminal's geographical position.Access to this service 40 may require equipment on each vehicle 11, 12,and 13, adapted to receive signals from one or more satellites and tocompute information that indicates a geographical position from thereceived signals. The network service may involve defining a grid withgrid lines 1001, 1002, 1003, and 1004, the grid covering a service areain which the network service is provided to the mobile terminals. Thegrid comprises tiles, such as tile 100, formed by respectively crossinggrid lines.

As shown, vehicle 11 is about to cross grid line 1003. Vehicle 11determines such a crossing based on position information retrieved fromthe positioning service 40 and the knowledge of the position andextension of grid line 1003. This may trigger crossing information to begenerated and sent via a related notification 91 (message) via a radiobase station 20 to the network side 30. The network side may thus beaware of vehicle 11 having just entered tile 100.

It is, therefore, able to maintain tile information for at least tile100, the information comprising identification information of the one ormore terminals (here the terminals on vehicles 11 and 12), when insidetile 100. In general, the terms vehicle, user, and mobile terminal areused synonymously, since a user may possess a mobile terminal, and amobile terminal may be on board of a vehicle operated by the user, sothat in the context of the present invention the geographical positionof all the vehicle, the user, and the mobile terminal usually coincide.

Once the network service is about to send a payload message to targetmobile terminals it can thus refer to the tile information fordetermining all target terminals. In this way, a payload message 92 canbe specifically sent to vehicles 11 and 12, whereas no communicationneeds to be performed with vehicle 12. An example may be thenotification of slippery road conditions inside tile 100, or, generally,any hazard X in front of vehicles 11 and 12. Since vehicle 13 hasalready passed by hazard X and is outside tile 100, no message 92 issent to this vehicle. In this way, not only bandwidth is saved, but alsothe driver of vehicle 13 is not distracted by receiving a message 92that is actually of no interest. In any way, the above concept makessure that all mobile terminals for which the respective payload messageis of interest receive the respective notification 92, whereas otherterminals are not disturbed/distracted by information that is notrelevant to them.

FIG. 1B shows a schematic view of a network system architectureaccording to another embodiment of the present invention. Specifically,the network service can be deployed in an operator's network system asexemplified in this FIG. 2 that depicts, as an exemplary deployment, anoverview in an UMTS environment. Besides the cellular network's core 301and RAN (radio access network) 302 it shows that part of the networkservice are provided by a network entity 310 that will be described ingreater detail in conjunction with the respective embodiments. Also,other subsystems and nodes 303 in the operator's network may beinvolved, wherein these other subsystems and nodes 303 may include aCell Broadcast Center (CBC), a Mobile Positioning System (MPS), and/or aBroadcast Multicast Service Center (BM-SC). Said core 301 may compriseGateway GPRS Support Node (GCSN), a Serving GPRS Support Node (SGSN),and/or a Home Location Register (HLR).

For providing the network service further service entities 304 can beemployed that send so-called GeoCast messages (GeoMessaging) to thesystem and with it to the vehicles 11, 12, etc. On the other hand, thevehicles may send their uplink messages directly to the service, and,additionally, the vehicles keep their location in synchronization with agrid database via sending the above-mentioned crossing information. Theservices 304 can be internal, i.e. part of the operator's network orrespective domain, so as to provide any payload destined for any servicearea via employing the network entity 310.

Furthermore, the shown architecture also allows for the services 304being external in the sense of not belonging to the operator's domain.In this way, the services 304 can be operated independently by externaloperators that do not have access to the tile information which can bemaintained internally, for example, in conjunction with the networkentity 310. As a consequence, the sensitive information on who is where(i.e. what mobile terminals are in what tile) does not need to leave thenetwork operator's domain. At the same time, however, the externalservices 304 provide the network service via registering to theoperator's network and, for example, providing some payload destined fora given service area. The actual forwarding of this payload to themobile terminals in this service area is then effected internally byentity 310, without the tile information being accessible to theservices 304.

In general, the vehicle density in a given area is assumed to have noimpact on the grid spacing but only on the capacity the network needs toprovide (bandwidth and radio, communication, and processing resources).Embodiments of the present invention envisage monitoring the mapping ofthe service areas to grid tiles, and, for example, if the ratio betweenan area mapped by the tiles and the service area, a split of the tile(s)along closer grid lines is considered. In turn any split tiles are agingand if no similar split decision would have been taken within a timeoutperiod (e.g. 1 hour), then the tiles are joined again. By this methodthe granularity of the grid, and there with the network load forlocalization, stays optimized to the current (GeoMessaging) usagepattern.

The above split procedure can be handled deferred or immediately. Forthe immediate split, all vehicles in a tile are informed immediately bya grid spacing update message about the split. Said grid spacing updatemessage may be some form of the above-mentioned information indictingthe position and the extension of the grid lines, now, however, relatedto closer grid lines. Thus, the vehicles will send their location updateaccordingly. In the deferred case, no extra grid spacing update messagesare sent and only vehicles newly entering the “old” tile will know aboutthe denser grid spacing. At this time, the information indicting theposition and the extension of the closer grid lines is conveyed to thesevehicles. The deferred approach will result in a smooth transition ofthe grid spacing without generating a peak in the network load. For ajoin of tiles the deferred method is the most meaningful.

FIGS. 2A to 2C show in a schematic fashion the splitting of tiles inline with embodiments of the present invention. The conventionalsituation as shown in conjunction with FIG. 2A is a possible startingpoint of the embodiments of the present invention. Specifically, thetiles 101, 102, 103, and 104 result from crossing grid lines 1101, 1102,1103, 1104, and 1105. The service area 200 is covered by tiles 101 to104. FIG. 2B shows the situation after splitting the tiles along thecloser grid lines 1111, 1112, 1113, and 1114, so as to produce splittiles 111 to 122. As becomes apparent from FIG. 2C, split tiles 112,113, 115, 116, 117, 119, 120, and 121 suffice to cover the service area200. In a way, the split resulted in a more efficient mapping of theservice area 200 to the tiles of the grid.

In general, reducing tile size will reduce the amount of user planemessages (payload), since all the vehicles or terminals that are insidethe remaining split tiles 111, 114, 118, 122, and 123 to 126, need notto be provided with the payload. However, reducing the tile size mayalso provoke a signalling increase with the possible constraint of theradio infrastructure capacity for the tile. Involved parameters alsoinclude the number of clients in the tile, payload message size (fromfew bytes to several kilobytes) and payload message frequency. Forexample, if the payload is tiny (only some tens of bytes), but thesignalling involved with a grid spacing update is comparatively large(some KB), the effectiveness of the split may need to be considered.Further, frequent small messages may not be as problematic as frequentlarge messages.

In this context, estimates regarding the savings on the payload side canbe carried out based on the single client. More clients in the tile willthen have an impact on the saving as a relative saving that staysconstant and as an absolute saving that increases linearly withvehicles' density. Therefore, the precision estimate may be higher for ahigher vehicle density.

The above split procedure is now described in the exemplary case of aC-ITS Application Server (C-ITS AS) that knows the so-called ServiceArea (SA) and a GeoMessaging Enabler that knows tiles. C-ITS is anacronym for Cooperative Intelligent Transport Systems whose applicationscover a wide range of different scenarios for road transport withentities in the infrastructure, in vehicles, and in portable devices.The related functional communication involves a variety of communicationtechnologies, such as ad-hoc communications (e.g. ITS-G5 standardized atETSI, equivalent to CALM M5 standardized at ISO), infra-red (IR)standardized at ISO and others such as millimeter radio waves, cellularnetwork communications (e.g. UMTS, LTE and other generations). AGeoMessaging Enabler is for example the Geolocation Messaging (TM)system of Ericsson Inc.

Both the C-ITS AS SA and the GeoMessaging Enabler tiles are equivalent,respectively, to the service area and tiles of the other embodiments ofthe present invention. Depending on the specific C-ITS AS configuration,the service area can be defined in terms of a static, fixed shape, ordynamic, i.e. it changes shape and/or position in the next message. Asfar as the split factor is concerned, a factor of 2 (i.e. 2 times 2split tiles) may be preferred. This situation corresponds to the splitshown in conjunction with FIGS. 2A and 2B. Nevertheless, also otherfactors, such as 3, may be employed, but such splitting may become moredifficult to handle as the grid gets more and more fragmented.

In general, the saving obtained by a tile split can be large forcomparatively small SAs (as compared to the tile size). For permanent orstatic target areas this may be reasonable, so that the GeoMessagingEnabler shall be informed from the C-ITS AS on whether a service area isstatic or dynamic. In the case of static SAs any timers for determininga possible later join should not age fast, since there is no dynamicprocess that would interfere with the split of tiles.

Furthermore, the C-ITS AS shall register static SAs at the GeoMessagingEnabler and provide information regarding usage pattern, comprising, forexample, an average message frequency, message size or payloadbandwidth. After registration, an SA can be identified and may be thusaddressable by a GUID reference (Globally Unique ID). The C-ITS AS theaddresses these target (service) areas by using such GUID. In general,complex shapes of SAs may require more signalling than simpler shapes,in the sense that a for example a rectangular SA can be easier handledalong with rectangular tiles.

In the following, a specific calculation on the split benefit isdescribed. It may be employed in embodiments of the present invention,for example, in conjunction with the determination of whether tiles aresplit or not. Again, the situation as shown in FIG. 2A serves as astarting point in that figure S1 represents the area of service area200, whereas figure S represents the sum area of tiles 101, 102, 103,and 104 which cover service area, and figure S2 represents the overheadwith S2=S−S1.

In FIG. 2B, that depicts situation after the split, the sum area oftiles 112, 113, 115, 116, 117, and 119 to 121 which cover service areacan be identified as S′. As is immediately apparent the residualoverhead S2′=S′−S1 is substantially less than overhead S2 before thesplit. The overhead is reduced by the sum area S2S of tiles 111, 114,118, 122, and 123 to 126 that do not cover the service area 200. Thissituation is emphasized in conjunction with FIG. 2C in which S′ is shownin diagonally hatched fashion and S2S is shown vertically hatchedfashion. Tile splitting saving S2S, i.e. the reduction of residualoverhead with tile splitting is the difference between S and S′, so thatS2S=S−S′.

As far as signalling is concerned, it is now considered the number oflocation (LOC) messages per time unit (second) in one tile. LOC messageswill be sent when a vehicle crosses a grid line as the above-mentionedcrossing information. For the sake of simplicity, only the vehicleswhich enter the tile are taken into account. Furthermore, the tile splitfactor is assumed to be 2 which cuts by half traveling distance to reachthe next tile. When traveling at the average speed this split tiledoubles the number of the LOC messages. With L being the border linelength of the tile, and P being the total border line length of an area,i.e. circumference of a tile or the sum of all Ls.

Therefore, one can define after the split

L′=0.5*L; and   (1)

P′=4*L′=4*0.5*L=2*L;   (2)

so, the total border line will be 2 times longer after the split, andtherewith 2 times more LOC messages will be generates as compared to theoriginal tile. If signalling load (achieved by tile splitting), islarger than the saving in payload (achieved by tile splitting), tilesplitting itself may not be sensible. A related process maycorrespondingly judge not to perform tile splitting.

However, LOC messages can be quite small, e.g. only 100 bytes in somecommon implementations. At the same time, signalling load can be wellestimated if the number of the vehicles in the area is known or can beestimated. Additionally, an average vehicle speed can be considered forstatistical purposes and history-based estimations. An absolute maximalvalue can be derived for the signalling load, if the total number ofroad lanes entering the tile is known. For a vehicle safety distance (inthe time domain) of, for example, 2 seconds,

LOC_MAX=(number of lanes)/2.   (3)

Assuming a highway intersection being located within the tile, threelanes in each direction will produce a maximum of (4*3)/2=6 LOC/s. Thiswill be a maximum figure in any feasible traffic situation.

On the other hand, signalling payload for such a highway intersectiontile can be approximated to be at maximum 600 bytes/s. A moreconservative guess will be 1 KB/s (B=byte), in case also a GRID updateoccurs as well. It is further assumed that there is at maximum one lanecrossing per 50 meters of tile border line (in the urban areas with highinfrastructure density). The estimation of a maximum signalling involvedis carried out for a tile with 1 km border line length, i.e. a tile withan area of 1 km². With the above density of one lane per 50 meters ofthe tile border line, on 1 km there is

$\begin{matrix}\begin{matrix}{{LOC\_ MAX} = {\left( {20\mspace{14mu} {lanes}*4\mspace{14mu} {sides}} \right)/2}} \\{= {40\mspace{14mu} {LOC}\text{/}s}}\end{matrix} & (4)\end{matrix}$

From the above, a maximum bandwidth BW_MAX for signalling within the 1km² tile can be estimated to be is 4 KB/s.

On the other hand, the estimation of the maximum signalling in theminimum tile size of 50 meters is LOC_MAX=4/2=2 LOC/s=200 B/s. Even forthe instance that such a small tile (50 meters*50 meters) contains alarge 3-lane road intersection, estimation of the maximum signallingwill be: LOC_MAX=12/2=6 LOC/s=600 B/s.

On the payload saving side, the number of vehicles in the tile can beconsidered. This may involve keeping statistics per tile within theGeoMessaging Enabler together with the above figure S2S, i.e. any figureindicating how many split tiles can be saved. Specifically, in casethree split tiles (out of four) are part of S2S, then a 75% saving isachieved with regard to the addressed terminals as compared to theoriginal tile. In case two split tiles (out of four) are part of S2S,then a 50% saving is achieved with regard to the addressed terminals ascompared to the original tile. Finally, in case one split tile (out offour) is part of S2S, only a 25% saving is achieved with regard to theaddressed terminals as compared to the original tile. In general, it isassumed that vehicles are distributed equally in the tile.

With the assumption of a statistical distribution of vehicles in onetile, the number of vehicles may correlate to the tile size. This maybe, however, valid only for large tiles and not for small tiles. In anyway, the statistic precision may be higher for the larger tiles.

In the following, a further example is given that considers a 500 metergrid with a corresponding tile size of 500 m×500 m. A signalling payloadfor all addressed vehicles in the tile is assumed to be maximum 8 KB/sbefore tile splitting. After tile splitting, signalling payload isassumed to be 16 KB/s. Further, payload in the tile is assumed to be 24KB/s.

With a 50% tile saving, i.e. two out of four split tiles are part ofS2S, the payload will be 12 KB/s. A total gain with tile splitting inthis case will be 12 KB/s−8 KB/s=4 KB/s. In terms of per cent, the totalsaving is 12.5% (4 KB/s/(24 KB/s+8 KB/s)). Assuming a threshold for tilesplitting decision to be X % but being lower than 12.5%, theGeoMessaging Enabler will perform tile splitting, whereas for X>12.5, notile splitting will take place.

FIG. 3 shows a possible timely evolution of the signalling 820 and thepayload 810 in Mbit/minute (axis 801) versus time in minutes (axis 802).

With again reference to FIG. 2C, split tiles can have specialdesignation names, which will reflect the original tile name. Forexample, tile 101 may have an associated name “T106”. Since tile 101 wassplit into four tiles, the resulting tiles 111, 112, 115, and 116 can bedenoted as “T106 a”, “T106 b”, “T106 c”, and “T106 d”. When an agingtimer expires, split tiles can be easily recomposed (joined) again totile 101 with denomination “T106”. If tile 112 with denomination “T106b” is split too, the four newly split tiles can have a names “T106 ba”,“T106 bb”, “T106 bc”, and “T106 bd”, respectively. Such naming can beapplied recursively. Extra tile names can be required for statisticalpurposes (identifiers). In any way, tiles are already unambiguouslydefined by their coordinates and size, so that the denomination bydedicated names can be optional.

In the following, dynamic service areas are considered. Specifically,improvements can be obtained in that a dynamic tile size saves onsignalling, payload, and load balancing. In such cases, a split decisionwill be taken every time when a message is coming in. With theimprovements on the signalling side one runtime parameter for the splitdecision may be the current payload. The better the payload's trafficpattern is known, the more precise a decision can be taken.

As already mentioned, embodiments of the present invention may employ aso-called aging timer whose expiry will result in re-joining thepreviously split tiles. For the case of permanent, static target areas,however, no aging timer may be necessary if there is information at handon the usage pattern. If no such information is available but if payloadtraffic statistics are available, a high aging timer value can be used.Again, the better the payload's traffic pattern is known, the moreprecise a decision on splitting can be taken. In turn, for more precisedecisions a longer aging timer value can be used than for less precisedecisions. In general, however, registered SAs aging timers shouldexpire if they are not used.

Moreover, criteria such as a minimum tile size and the reduction of thelocation update frequency may also apply. For example, GPS has aneffective precision of 10 meters, so this size will be absolute minimumtile size. Further, with an average speed of 40 km/h, and a tile size of650 meters, a tile can be traversed by a vehicle within 60 seconds.Therefore, the minimum tile size can be put to 100 meters and in thiscase a LU (location update) occurs every 10 seconds per vehicle.

By splitting the tile(s), some payload can be saved at the cost of anincreased signalling. Both signalling and payload depends of number ofvehicles in the tile (service area). A maximum payload is calculated tobe 4 KB/s for a 1 km² tile. This figure is being doubled by each splitas can be deduced from the calculations above. In addition, there may bethe need for statistical purposes to collect maps database, and toconclude when a tile intersects a road lane. Also, there may be a needto perform further statistics, e.g. on the number of LOC messages persecond and per tile.

According to a further embodiment, it may be considered how many roadlines intersect with an original tile. From the minimum securitydistance (in the time domain), e.g. 2 seconds, it can be derived thatthere are at maximum 0.5 LOC messages per second and per lane. If theservice area is given an identifier (ID), statistics can be collectedper each ID. If an aging timer is required for newly split tiles, suchstatistic measurement can be of benefit and should be thereforecollected.

In general, an involved database should contain/store the followinginformation and corresponding entries: a tile ID, tile coordinates, atile size, an aging timer, an SA database registry that contains apre-calculated mapping of SAs to tiles and that are statistically split,an SA aging timer, any SA GUIDs, an average payload (e.g. in Mbit perminute in terms of a sliding window), a tile splitting threshold (e.g.in per cent [%]), an old tile ID, a new tile ID, a payload saving pertile split (e.g. in terms of a statistic, which can be only the savingwhich leads to the split decision), and an residual overhead (should bea property of one SA). In addition, a database history can be kept, e.g.within the GeoMessaging Enabler, for certain period of time. Further, anabsolute payload statistics could be kept on a gliding average (e.g. inone minute window).

In the following, aspects of communicating the tile splitting towardsthe vehicles (mobile terminals) are described. It can be assumed thatwithin one grid 100 to 1000 different service areas can coexist. It maythen be important to cross-compare the size of the service area versusthe corresponding tile area. If there is a lot of overhead, then a splitof the tile (e. g. with factor 2) can be considered to reduce theoverhead, wherein such splitting of the tile is not related to theinfrastructure or to number of radio channels available. Afterconsidering the splitting of the tile, the possible saving iscalculated: if the achievable saving is above a predefined threshold,tile split is justified and the splitting of the tile can be actuallyexecuted, e.g. within GeoMessaging Enabler. For static SAs, acorresponding split decision can be taken at the time of registration.

If the C-ITS AS provides information on the usage, tile split will beperformed immediately. If not, just the mapping can be stored and asplit will be decided based on the traffic statistic. Any tile splittingwill affect only the future messages sent from the C-ITS AS. In any way,however, the vehicles should be aware of the tile split for which thereare basically two methods to inform the vehicles:

Firstly, a broadcast can be employed to notify the split to thevehicles. This option will cause a peak in the signalling load, since agiven number of terminals must be informed of the split at the same timeor within a given (short) period of time. It may be useful to define apeak signalling load as a threshold, which is related to the networkcapacity in a certain area (e.g. 200 B/terminal). FIG. 4A shows such ascenario in terms of broadcast capacity (axis 803) versus time inseconds (axis 804).

If the broadcast option causes a peak signalling load which is higherthan the threshold value, the broadcast could be sent in waves or timeslots as depicted in FIG. 4B. Such a procedure is able to flatten thepeak signalling load. For related calculations one or more of thefollowing parameters can be taken into account: maximum number ofmessages to be sent for broadcast; number of the targets in the certaintile; and number of waves/time slots.

For example, if the specified threshold for a peak load in one tile is1000 clients in cell per second that can be reached, and there are 2500clients in that tile, the following calculation can be carried out: (1)20% safety margin from peak load: 80%*1000 clients in cell/second=800clients in cell/second can be addressed; (2) there is a total 2 500clients in the tile; and (3) 2 500/800=3.125 means that four waves ortime slots are needed (in the first three waves 800 clients will bereached, and in the fourth wave the remaining 100 clients will bereached. As an example, one can consider Germany where there is anaverage vehicle density of 140 vehicles/km², taken from 50 millionvehicles and 375000 km². This would include, however, all vehicles andnot only the ones on the road, but also the ones parked and currentlyunused.

The second option is to inform a vehicle when the new tile border iscrossed (so-called “lazy split”). In this case, no broadcast messagewill be necessary, but, when a new vehicle crosses the border to thenewly split tile, signalling exchange will occur between theGeoMessaging Enabler/Registry and the respective vehicle. Also thisapproach is able to flatten the signalling involved with the tile split.

FIG. 5 shows a flowchart representation of method embodiments of thepresent invention. This method embodiment is for providing a networkservice to a plurality of mobile terminals inside a service area, themobile terminals being arranged to communicate with a cellularcommunication network and the service area being a part of ageographical area that is covered by the cellular communication network.The method comprises a step S10 of defining a grid with grid lines,wherein the grid covers the service area with one or more tiles framedby the grid lines. The method comprises a step S20 of determiningwhether there is at least one split tile that results from splitting theone or more tiles along closer grid lines and that does not overlap withthe service area. The method comprises a step of S30 of splitting theone or more tiles along the closer grid lines based on the determining.The method also comprises a step S40 of providing the network service inthe split tiles that cover the service area.

FIG. 6 shows a schematic view of a network entity in communication witha network according to another embodiment of the present invention. Inthe sense of the present invention, an entity can be any of a dedicatedpiece of hardware, a share of hardware that is used by various processesand tasks, a collection of distributed pieces or shares of hardware. Inthis way, involved processing units and possibly also memory units canbe dedicated, shared, or distributed.

According to this embodiment a network entity 310 is configured toprovide a network service to a plurality of mobile terminals inside aservice area, the mobile terminals being arranged to communicate with acellular communication network and the service area being a part of ageographical area that is covered by the cellular communication network.The network entity 310 comprises a processing unit 311 that can executecode stored in a memory unit 312. In this way, the code may instruct theprocessing unit 311 to define a grid with grid lines, the grid coveringthe service area with one or more tiles framed by the grid lines, todetermine whether there is at least one split tile that results fromsplitting the one or more tiles along closer grid lines and that doesnot overlap with the service area, to split the one or more tiles alongthe closer grid lines based on the determination whether there is atleast one split tile, and to provide the network service in the splittiles that cover the service area. The network entity 310 may alsocomprise a communication unit 313 that is configured to communicate witha network system, such as the network 30 of the other embodiments of thepresent invention.

The embodiments of the present invention can provide several advantagesover the conventional techniques. In particular, adapting the tile sizeto dynamic conditions can result in saving in total cost of ownership ofthe system/service in that less bandwidth will be needed. Further,statistical data can be collected that was not available before. Stillfurther, a more precise geographical addressing and/or an easieraddressing for the static SAs can be achieved.

Although detailed embodiments have been described, these only serve toprovide a better understanding of the invention defined by theindependent claims, and are not to be seen as limiting.

1. A method for providing a network service to a plurality of mobileterminals inside a service area, the mobile terminals being arranged tocommunicate with a cellular communication network and the service areabeing a part of a geographical area that is covered by the cellularcommunication network, the method comprising the steps of: defining agrid with grid lines, the grid covering the service area with one ormore tiles framed by the grid lines; determining whether there is atleast one split tile that results from splitting the one or more tilesalong closer grid lines and that does not overlap with the service area;splitting the one or more tiles along the closer grid lines based on thedetermining; providing the network service in the split tiles that coverthe service area; and notifying mobile terminals of the split one ormore tiles via a broadcast to the mobile terminals, whereincommunication resources related to performing the broadcast are comparedto a threshold, and wherein the broadcast is performed in waves ofbroadcasts or time slots when the threshold is exceeded.
 2. The methodof claim 1, further comprising: joining the split one or more tiles; andnotifying mobile terminals of the split one or more tiles that have nowbeen joined.
 3. The method of claim 1, further comprising a step ofestimating savings in communication resources, generated by splittingthe one or more tiles along the closer grid lines, wherein the splittingis further based on a result of the estimating.
 4. The method of claim1, further comprising: determining the threshold based on a peaksignalling load value defined for the service area.
 5. The method ofclaim 4, wherein the threshold is determined based on a broadcastcommunication capacity in the service area.
 6. The method of claim 1,wherein the notifying mobile terminals of the split one or more tilesvia a broadcast to the mobile terminals, comprises: for each of the oneor more tiles, determining a number of mobile terminals in the tile thatare to receive the broadcast notification, determining a number of timeslots to be used to broadcast the notification to the mobile terminalsin the tile based on the determined number of mobile terminals in thetile, and selecting the time slots for use in the broadcast notificationto the mobile terminals in the tile so that the broadcast notificationis completed to the mobile terminals in the tile in the determinednumber of time slots.
 7. The method of claim 1, wherein the notifyingmobile terminals of the split one or more tiles via a broadcast to themobile terminals, comprises: for each of the one or more tiles,determining a number of mobile terminals in the tile that are to receivethe broadcast notification; determining a number of waves of broadcastnotifications to be sent to corresponding different groups of the mobileterminals in the tiles based on the determined number of mobileterminals in the tiles; and sending waves of broadcast notifications todifferent groups of the mobile terminals in the tiles so that thebroadcast notifications are completed to the mobile terminals in thedetermined number of waves.
 8. The method of claim 1, wherein theservice area is one of C-ITS application server service areas.
 9. Themethod of claim 1, wherein the grid fields and the split grid fields aredefined as grid fields of a geomessaging enabler.
 10. A network entityfor providing a network service to a plurality of mobile terminalsinside a service area, the mobile terminals being arranged tocommunicate with a cellular communication network and the service areabeing a part of a geographical area that is covered by the cellularcommunication network, the network entity comprising: at least oneprocessor; and at least one memory coupled to the at least one processorand which stores program code that when executed by the at least oneprocessor causes the at least one processor to perform operations to:define a grid with grid lines, the grid covering the service area withone or more tiles framed by the grid lines; determine whether there isat least one split tile that results from splitting the one or moretiles along closer grid lines and that does not overlap with the servicearea; split the one or more tiles along the closer grid lines based onthe determination whether there is at least one split tile; provide thenetwork service in the split tiles that cover the service area; andnotify mobile terminals of the split one or more tiles via a broadcastto the mobile terminals, wherein communication resources related toperforming the broadcast are compared to a threshold, and wherein thebroadcast is performed in waves of broadcasts or time slots when thethreshold is exceeded.
 11. The network entity of claim 10, wherein theat least one processor further performs operations to: join the splitone or more tiles; and notify mobile terminals of the split one or moretiles that have now been joined.
 12. The network entity of claim 10,wherein the at least one processor further performs operations to:estimate savings in communication resources, generated by splitting theone or more tiles along the closer grid lines, wherein the splitting isfurther based on a result of the estimating.
 13. The network entity ofclaim 10, wherein the at least one processor further performs operationsto: determine the threshold based on a peak signalling load valuedefined for the service area.
 14. The network entity of claim 13,wherein the threshold is determined based on a broadcast communicationcapacity in the service area.
 15. The network entity of claim 10,wherein the operation to notify mobile terminals of the split one ormore tiles via a broadcast to the mobile terminals, comprises: for eachof the one or more tiles, determining a number of mobile terminals inthe tile that are to receive the broadcast notification, determining anumber of time slots to be used to broadcast the notification to themobile terminals in the tile based on the determined number of mobileterminals in the tile, and selecting the time slots for use in thebroadcast notification to the mobile terminals in the tile so that thebroadcast notification is completed to the mobile terminals in the tilein the determined number of time slots.
 16. The network entity of claim10, wherein the operation to notify mobile terminals of the split one ormore tiles via a broadcast to the mobile terminals, comprises: for eachof the one or more tiles, determining a number of mobile terminals inthe tile that are to receive the broadcast notification; determining anumber of waves of broadcast notifications to be sent to correspondingdifferent groups of the mobile terminals in the tiles based on thedetermined number of mobile terminals in the tiles; and sending waves ofbroadcast notifications to different groups of the mobile terminals inthe tiles so that the broadcast notifications are completed to themobile terminals in the determined number of waves.
 17. The networkentity of claim 10, wherein the service area is one of C-ITS applicationserver service areas.
 18. The network entity of claim 10, wherein thegrid fields and the split grid fields are defined as grid fields of ageomessaging enabler.
 19. A computer program product for providing anetwork service to a plurality of mobile terminals inside a servicearea, the mobile terminals being arranged to communicate with a cellularcommunication network and the service area being a part of ageographical area that is covered by the cellular communication network,the computer program product comprising a non-transitory computerreadable medium storing program code, the program code, when executed byat least one processor causes the at least one processor to performoperations comprising: defining a grid with grid lines, the gridcovering the service area with one or more tiles framed by the gridlines; determining whether there is at least one split tile that resultsfrom splitting the one or more tiles along closer grid lines and thatdoes not overlap with the service area; splitting the one or more tilesalong the closer grid lines based on the determining; providing thenetwork service in the split tiles that cover the service area; andnotifying mobile terminals of the split one or more tiles via abroadcast to the mobile terminals, wherein communication resourcesrelated to performing the broadcast are compared to a threshold, andwherein the broadcast is performed in waves of broadcasts or time slotswhen the threshold is exceeded.
 20. The computer program product ofclaim 19, wherein the operations further comprise: joining the split oneor more tiles; and notifying mobile terminals of the split one or moretiles that have now been joined.